The present invention generally relates to the thrust bearing structure of a scroll compressor to be used as a fluid compressor for a refrigeration or air conditioning unit, etc.
The operating principle and the basic structure of a scroll compressor will be described with reference to FIG. 9 and FIG. 10.
When the orbiting scroll member 3 is caused to undergo orbiting motion (arrow A) and the rotation thereof is prevented, with spirally shaped wraps 1a, 1b of substantially the same shape provided on plates 2a, 2b of the orbiting scroll members and fixed scroll member 4 being mutually engaged, the volume of fluid sucked in from the suction opening 5 is gradually reduced in a reduction chamber 6 (6a, 6b) delimited by the orbiting scroll member 3 and the fixed scroll member 4 so as to increase its pressure before discharging it through the discharge opening 7.
A rotation preventing mechanism 9 is provided between the orbiting scroll 3 and a frame 8. A crank shaft 11, rotatably supported on a bearing 10 which is disposed at the center of the frame 8, is engaged at one end thereof with a rotary shaft 12 of the orbiting scroll member 3 and is rotatably driven by a driving source 13 such as motor or the like. The fluid sucked in from the suction opening 5 is compressed within the compression chamber 6, is discharged through the discharge opening 7 and flows into the discharge pipe 14. These elements are accommodated in a closed casing. Lubricating oil 16 stored in the bottom portion of the casing 15 is fed into the upper portion of the casing through through-hole 18 by a pump mechanism 17 at the lower end of the crank shaft 11.
Also, a sliding surface 19 is formed on the frame 8 opposite to the rear surface of the orbiting scroll member 3 so as to prevent both the scroll members 3, 4 from being separated by the pressure in the compression chamber 6.
In such a scroll compressor, the fluid pressure generated in the compression chamber 6 by the orbiting motion A of the scroll member 3, as shown in FIG. 11, acts at point G half-way up the wraps 2a, 2b and generates a compression force FG. The force FS for orbiting the orbiting scroll member 3 acts on the side of orbiting scroll member 3 opposite the wraps at point S to create a reaction force on the crank shaft 11 which is in system contact. Therefore, the action point G of the fluid pressure and the action point S of the orbiting force are spaced in the axial direction of the compressor, and the forces FG and FS act in directly opposite directions, whereby a moment M is generated. The moment M acts in a direction tending to tilt the orbiting scroll member 3, with a result that a strong thrust force FJ is locally applied to the sliding surface 19 of the frame 8. The deviation of such thrust force FJ causes deleterious effects such as an abnormal abrasion of the sliding face, loss due to increases in sliding friction, an unstable axial thrust force, unstable orbiting motion of the orbiting scroll member and so on.